In an interview with Comic Book Resources, Millar says this isn’t quite the case and the reports were blown out of proportion.
According to Millar’s interview with CBR:
In all honesty, the story has been massively misreported. There is no issue at all here. Someone simply saw that the image we had planned for the first cover had been removed and assumed DC had hit us with a writ or something. Nothing could be further from the truth, and the whole thing is much more informal. What happened was that someone in DC editorial was a little worried that we were casually mentioning two of their characters in interviews and asked legal to ask us not to. The legal guys at DC, who are friends of mine, just dropped me a casual, informal email asking me to be cool, and I agreed, promising them that Steve and I wouldn’t cross any kind of line in the promotion of ‘Nemesis.’
Steve and I both have a good relationship with DC, and I’m friends with about half the staff. So we chatted about it and as a courtesy removed the cover image we planned, which we both felt might just be a little too playful. DC knew this was a gesture of goodwill and appreciated it, but they absolutely didn’t ask us to remove it. Everyone is on very good terms, and there is absolutely no issue here.